leetcode709

class Solution {
    public String toLowerCase(String str) {
        StringBuilder s = new StringBuilder(str);
        for(int i=0;i<str.length();i++){
            char c = str.charAt(i);
            if (c>=65 && c<=90){
                s.setCharAt(i,(char)(c+32));
            }
        }
        return s.toString();
    }
}